Nirsevimab
Nirsevimab is a monoclonal antibody used to prevent RSV (respiratory syncytial virus) lower respiratory tract disease in newborns, infants, and young children up to 24 months old.
🧬 Where this information comes from
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 1 clinical label set within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
Nirsevimab (Beyfortus) is a lab-made antibody, not a vaccine, that protects newborns, infants and at-risk toddlers from serious RSV lung infection by blocking the F protein the virus uses to enter lung cells; on the U.S. market since about 2023, it is now widely used. Most babies handle it well, and the usual side effects are a rash or soreness, redness or swelling where it was given. The one thing to watch for is a serious allergic reaction (hives, trouble breathing, bluish skin or sudden limpness), which needs emergency help right away. One dose lasts about 5 months, so timing it to the start of RSV season matters.
Clinical pearls
- Before the thigh shot, mention any bleeding disorder, low platelets or blood thinner, since muscle injections can bleed more.
- Routine baby vaccines can be given at the same visit, just in a separate syringe and a different spot.
- A child who gets Beyfortus this season should not also get palivizumab (Synagis), the older RSV antibody shot.
- Mention any RSV vaccine you got during pregnancy; most of those babies do not also need Beyfortus.
Patient Information Guide A plain-language walkthrough of Nirsevimab, written from its FDA label.
What Nirsevimab Is Used For
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Nirsevimab (brand name Beyfortus) is approved to prevent RSV lower respiratory tract disease — serious lung illness caused by respiratory syncytial virus — in young children. It is not a treatment for RSV once illness has started.
- Beyfortus injection: Prevention of RSV lower respiratory tract disease in newborns and infants born during or entering their first RSV season
- Beyfortus injection: Prevention of severe RSV disease in children up to 24 months old who remain vulnerable going into their second RSV season
- Beyfortus injection: Used in high-risk children — including those with chronic lung disease of prematurity or hemodynamically significant congenital heart disease (a serious structural heart condition) — during their first or second RSV season
- Beyfortus injection: An additional dose is recommended for children undergoing cardiac surgery with cardiopulmonary bypass (a heart-lung machine) to maintain protective antibody levels after surgery
How Nirsevimab Works
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Nirsevimab is a monoclonal antibody — a lab-engineered protein designed to act like a very specific immune defender. It targets the RSV F (fusion) protein, the structure the virus uses to latch onto and enter the cells lining the lower airways. By binding tightly to this protein, nirsevimab blocks the virus from fusing with and infecting lung cells, preventing the lower respiratory tract disease RSV can cause in young children.
Because RSV can mutate, some viral variants have shown reduced sensitivity to nirsevimab in laboratory testing. However, resistance-associated variants have been rare in real-world surveillance, and most binding-site amino acids on the RSV F protein remain highly conserved — meaning the target is very stable across most circulating strains.
Nirsevimab Dosage
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Beyfortus is given as a single intramuscular (IM) injection — always by a healthcare provider, never at home. For infants in their first RSV season, the dose is based on body weight. Children at high risk entering their second RSV season receive two injections given at the same visit. For children undergoing cardiac surgery with cardiopulmonary bypass, an additional dose may be recommended after surgery.
- Administered once per RSV season for most children
- Given preferably into the anterolateral (outer) thigh
- Timing is planned around the start of RSV season to maximize the roughly 5 months of protection a single dose provides
- Follow the prescriber's guidance on exact timing — especially if your child was born prematurely or has a qualifying heart or lung condition
Dosing details from the FDA-approved label
From the Nirsevimab prescribing information (“Dosage and Administration”). Doses are set by your prescriber for your product, condition, kidney function and age — never change a dose on your own.
- Neonates and infants born during or entering their first RSV season, less than 5 kg body weight
- 50 mg by IM injection, as a single intramuscular injection
- For neonates and infants born during the RSV season, administer starting from birth; for those born outside the RSV season, administer once prior to the start of the RSV season
- Neonates and infants born during or entering their first RSV season, 5 kg and greater body weight
- 100 mg by IM injection, as a single intramuscular injection
- For neonates and infants born during the RSV season, administer starting from birth; for those born outside the RSV season, administer once prior to the start of the RSV season
- Children up to 24 months of age who remain at increased risk for severe RSV disease in their second RSV season
- 200 mg administered as two IM injections of (2 × 100 mg)
- Regardless of body weight
- First RSV season: children undergoing cardiac surgery with cardiopulmonary bypass, surgery within 90 days after receiving BEYFORTUS
- Additional IM dose as soon as the child is stable after surgery, based on body weight at the time of the additional dose (Table 1: 50 mg if less than 5 kg
- 100 mg if 5 kg and greater)
- Weight-based dosing per Table 1
- First RSV season: children undergoing cardiac surgery with cardiopulmonary bypass, more than 90 days since receiving BEYFORTUS
- Additional dose of 50 mg as an IM injection, as soon as the child is stable after surgery
- Regardless of body weight
- Second RSV season: children undergoing cardiac surgery with cardiopulmonary bypass, surgery within 90 days after receiving BEYFORTUS
- Additional dose of 200 mg as an IM injection, as soon as the child is stable after surgery
- Regardless of body weight
- Second RSV season: children undergoing cardiac surgery with cardiopulmonary bypass, more than 90 days since receiving BEYFORTUS
- Additional dose of 100 mg as an IM injection, as soon as the child is stable after surgery
- Regardless of body weight
Read the label’s full dosing text
2 DOSAGE AND ADMINISTRATION Administer as an intramuscular injection. ( 2.1 ) Recommended dosage: Neonates and infants born during or entering their first RSV season: 50 mg if less than 5 kg in body weight. ( 2.1 ) 100 mg if greater than or equal to 5 kg in body weight. ( 2.1 ) Children who remain vulnerable through their second RSV season: 200 mg (2 × 100 mg injections). ( 2.1 ) 2.1 Recommended Dosage First RSV Season for Neonates and Infants For neonates and infants born during the RSV season, administer BEYFORTUS starting from birth. For neonates and infants born outside the RSV season, administer BEYFORTUS once prior to the start of the RSV season considering duration of protection provided by BEYFORTUS [see Clinical Pharmacology (12.2) ] . The recommended dosage of BEYFORTUS for neonates and infants born during or entering their first RSV season is based on body weight (see Table 1 ) and is administered as a single intramuscular (IM) injection. Table 1 Recommended Dosage of BEYFORTUS for the First RSV Season Body Weight at Time of Dosing Recommended Dosage Less than 5 kg 50 mg by IM injection 5 kg and greater 100 mg by IM injection Second RSV Season for Children Who Remain at Increased Risk for Severe RSV Disease For children up to 24 months of age, regardless of body weight, who remain at increased risk for severe RSV disease in their second RSV season, refer to Table 2 below for recommended dosage. Table 2 Recommended Dosage of BEYFORTUS for the Second RSV Season for Children Who Remain at Increased Risk for Severe RSV Disease Child's Age at Time of Dosing Recommended Dosage Up to 24 months of age Regardless of body weight 200 mg administered as two IM injections of (2 × 100 mg) First and Second RSV Season for Children Undergoing Cardiac Surgery with Cardiopulmonary Bypass For children undergoing cardiac surgery with cardiopulmonary bypass, an additional dose of BEYFORTUS is recommended as soon as the child is stable after surgery to ensure adequate nirsevimab-alip serum levels. The recommended dosage of BEYFORTUS is administered as an IM injection. First RSV season: If surgery is within 90 days after receiving BEYFORTUS, the additional dose should be based on body weight at the time of the additional dose. Refer to Table 1 for weight-based dosing.
Excerpted — the section continues on the label. Read the full Dosage and Administration section on DailyMed →
Nirsevimab Side Effects
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Beyfortus is generally well tolerated — most children in clinical trials who had any reaction (about 1.2%) experienced mild to moderate effects.
Common side effects
- Rash (including flat or raised spots on the skin)
- Injection site reaction (pain, swelling, redness, or firmness where the shot was given)
- Rash (flat, raised, or blotchy spots on the skin) — reported in about 0.9% of children receiving Beyfortus
- Injection site reaction (pain, swelling, firmness, or redness where the shot was given) — reported in about 0.3%
When to get medical help
- Call for emergency help immediately if your child shows signs of a severe allergic reaction: hives, trouble breathing, bluish skin color, or sudden limpness
- Tell the healthcare provider before the injection if your child has a bleeding disorder, low platelet count, or takes blood thinners — the shot may carry extra bleeding risk
Serious allergic reactions, including anaphylaxis, are rare but have been reported — signs include hives, trouble breathing, bluish skin, or sudden limpness. Seek emergency care immediately if any of these appear after the injection.
Nirsevimab Warnings and Precautions
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- Serious allergic reactions / anaphylaxis: Beyfortus has been associated with serious hypersensitivity reactions, including hives (urticaria), difficulty breathing (dyspnea), bluish skin color (cyanosis), and sudden muscle limpness (hypotonia). Anaphylaxis — a life-threatening whole-body reaction — is a known risk with this class of antibody. The injection must be given in a healthcare setting where treatment is immediately available.
- Bleeding disorders: Because Beyfortus is given as an intramuscular injection, it should be used with caution in children with thrombocytopenia (low platelet count), any clotting disorder, or those receiving anticoagulation (blood-thinning) therapy. The provider should take appropriate precautions.
- Not for adults: The safety and effectiveness of Beyfortus have not been established in adults. It is not indicated for use in adults or females of reproductive potential.
Nirsevimab Interactions
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Beyfortus has few known drug interactions, but there are important co-administration rules to follow:
- Childhood vaccines: Beyfortus can be given at the same visit as routine childhood vaccines — but always in a separate syringe at a different injection site. Never mix them in the same syringe or vial.
- Palivizumab (Synagis): Do not give palivizumab to a child who has already received Beyfortus during the same RSV season. Beyfortus may be used in a subsequent RSV season for children who received palivizumab in a prior season.
- Other immunoglobulin products: There is no information on using Beyfortus alongside other immunoglobulin products — consult the healthcare provider before combining.
- RSV diagnostic tests: Nirsevimab does not interfere with RT-PCR or rapid antigen RSV tests that use commercially available antibodies targeting standard sites on the RSV F protein.
Interactions listed in the FDA-approved label
From the Nirsevimab prescribing information (“Drug Interactions”): what the manufacturer studied or reported to the FDA.
- RT-PCR or rapid antigen detection RSV diagnostic assays: Nirsevimab-alip does not interfere with RT-PCR or rapid antigen detection RSV diagnostic assays that employ commercially available antibodies targeting antigenic site I, II, or IV on the RSV fusion (F) protein. For immunological assay results which are negative when clinical observations are consistent with RSV infection, it is recommended to confirm using an RT-PCR-based assay.
Read the label’s full interactions text
7 DRUG INTERACTIONS 7.1 Interference with RT-PCR or Rapid Antigen Detection RSV Diagnostic Assays Nirsevimab-alip does not interfere with reverse transcriptase polymerase chain reaction (RT-PCR) or rapid antigen detection RSV diagnostic assays that employ commercially available antibodies targeting antigenic site I, II, or IV on the RSV fusion (F) protein. For immunological assay results which are negative when clinical observations are consistent with RSV infection, it is recommended to confirm using an RT-PCR-based assay.
Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.
Before Taking Nirsevimab
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- Serious prior allergic reaction: Beyfortus is contraindicated — meaning it must NOT be given — to any child with a history of anaphylaxis or serious hypersensitivity to nirsevimab-alip or any ingredient in the product
- Bleeding disorders: Tell the provider if the child has low platelets (thrombocytopenia), a clotting disorder, or takes blood thinners — extra caution is needed with any IM injection
- Age limits: Safety and effectiveness have not been established in children older than 24 months — it is not approved for that age group
- Immunocompromised children: Beyfortus has been studied in a small number of children with a wide variety of immune-compromising conditions; the safety profile was consistent with other trials, but discuss the child's specific immune situation with the prescriber
- Adults and pregnancy/breastfeeding: Beyfortus is not indicated for adults or for females of reproductive potential
Nirsevimab Overdose
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There is limited experience with Beyfortus overdose, and no specific antidote exists. If an overdose occurs, the child should be monitored for any adverse reactions and treated based on symptoms. Contact a healthcare provider or poison control immediately if an overdose is suspected.
What Nirsevimab Does in the Body
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After a single dose of Beyfortus, higher levels of nirsevimab in the blood are linked to a lower chance of developing medically attended RSV lower respiratory tract infection. Protection from a single dose lasts approximately 5 months based on clinical data. In adult studies (for research purposes only, since Beyfortus is not approved for adults), RSV-neutralizing antibody levels rose to about 4 times baseline within 8 hours of injection and peaked by day 6.
How Your Body Processes Nirsevimab
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Beyfortus is given by intramuscular injection and reaches peak concentration in the bloodstream at a median of 6 days after the dose, with an estimated bioavailability of 84%. It has a long half-life of approximately 71 days, meaning it stays in the body for an extended period — which is why a single dose can protect through an RSV season. Nirsevimab is broken down by the body's normal protein-degrading pathways into small peptides, similar to how other antibodies are processed, and is not metabolized by the liver enzymes that process most traditional medications.
How to Store Nirsevimab
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Store refrigerated between 36°F to 46°F (2°C to 8°C). refrigerator, BEYFORTUS must be used within 48 hours or discarded. Store BEYFORTUS in original carton to protect from light until time of use.
Written from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
Nirsevimab: Pharmacist Answers to Common Questions
Quick, plain-English answers to the questions patients ask most about Nirsevimab — the kind of thing our pharmacy team would talk through with you at the counter.
What exactly does Beyfortus do — is it a vaccine?
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How is it given, and does my baby need more than one shot?
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What side effects should I watch for after my baby gets the shot?
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Can my baby get their routine vaccines at the same appointment as Beyfortus?
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My baby is premature — can they still get Beyfortus?
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My child had palivizumab (Synagis) last RSV season — can they get Beyfortus this season?
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Is Nirsevimab available over the counter?
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When was Nirsevimab first available?
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Answers drafted from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
More About Nirsevimab on HelloPharmacist
Nirsevimab Forms and Strengths (How It Comes)
Nirsevimab is available in 1 form. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.
Need a version that does not list lactose, a gluten source, a dye or gelatin? Inactive ingredients differ by manufacturer: see Nirsevimab inactive ingredients by manufacturer.
Injection
How this form is used
- Beyfortus injection is used to prevent RSV lower respiratory tract disease in newborns and infants entering their first RSV season
- Beyfortus injection is used to prevent severe RSV disease in children up to 24 months old who remain vulnerable going into their second RSV season
- Beyfortus injection is used in children with chronic lung disease of prematurity or hemodynamically significant congenital heart disease entering their first or second RSV season
- Beyfortus must be administered by a healthcare provider as an intramuscular injection, preferably into the anterolateral (outer) thigh — not the gluteal (buttock) muscle
- Beyfortus is available in 50 mg and 100 mg pre-filled syringes; the correct strength is selected based on body weight (first season) or age/risk (second season) — always check the label before use
- When given at the same visit as injectable childhood vaccines, Beyfortus must be injected with a separate syringe at a different site — never mixed in the same syringe or vial
- Do not use a Beyfortus pre-filled syringe if it has been dropped or damaged, the carton seal is broken, the solution is cloudy or discolored, or the expiration date has passed
Nirsevimab on the U.S. Market: Products, Makers and Brands
How Nirsevimab appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
1 company lists 2 Nirsevimab product records with the FDA, mostly as injection; the earliest marketing or approval year on record is 2023. Brand names on the directory include Beyfortus; the rest are generics.
Also listed with the FDA, not a patient dose form: Unfinished injection (4) · Unfinished injection, solution (4) · Unfinished liquid (1) — bulk drug substance and unfinished product sold to compounders and other manufacturers to finish, and multi-item kits. These aren’t counted in the dose-form total above.
Compare Nirsevimab Products
A representative set of FDA-listed product records for Nirsevimab — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Strength | Route | Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|---|---|
| 💊Injection | ||||
| 100 mg/mL | Intramuscular | Sanofi Vaccines US Inc. × 2 listings | BLA | View NDC → |
Showing 2 of 2 products — FDA National Drug Code Directory. See every product, package size and price: browse all 2 Nirsevimab NDCs →
Nirsevimab Side Effects Reported to the FDA (FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Nirsevimab — a signal of what to watch for, not proof the drug caused it.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Nirsevimab in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
Nirsevimab FDA Approval History
How Nirsevimab went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
Nirsevimab Recall History
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
The FDA’s enforcement reports list no Nirsevimab recalls since July 2021.
✅No Nirsevimab recalls on record since July 2021Source: FDA enforcement (recall) reports, via openFDA; our copy was last updated Oct 8, 2026.
RxNorm Concept Web — From Ingredient to Every Form and Strength
This page starts with one ingredient concept (IN). The branches below show its dose-form concepts (SCDF), then the available clinical drug and strength concepts (SCD). Combination products remain separate concepts with their own pages.
RxCUI 2642401 1 dose form · 2 strengths
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Dose form (SCDF) Prefilled Syringe RxCUI 2642405In current FDA listingsClinical drug / strength (SCD) 0.5 ML nirsevimab-alip 100 MG/MLRxCUI 26424061 ML nirsevimab-alip 100 MG/MLRxCUI 2642414
Look up RxCUI 2642401 in the RxCUI Atlas →
RxNorm is the U.S. National Library of Medicine’s normalized drug vocabulary. Its concept hierarchy can include forms that are not currently marketed; the status on each branch compares that concept with current FDA listings. RxCUIs identify vocabulary concepts, not individual packages or manufacturers.
Nirsevimab Supply and Shortage Status
Whether Nirsevimab is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
Nirsevimab Brand Names
Nirsevimab is sold under one brand name in the FDA directory — Beyfortus. A brand and its generic contain the same active ingredient; the brand name belongs to one company's product.
Who Makes Nirsevimab: Manufacturers and Labelers
One company lists Nirsevimab products with the FDA. By number of product records, the largest are Sanofi Vaccines US Inc.. Labelers include manufacturers and repackagers; the product in your bottle depends on which one your pharmacy stocks.
Nirsevimab Drug Class (RxNorm)
Nirsevimab belongs to the Respiratory Syncytial Virus Anti-F Protein Monoclonal Antibody class.
Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.
Sources for This Nirsevimab Page
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How this page is built
HelloPharmacist combines public FDA and NLM records and does not author the underlying clinical facts. The plain-language sections are written with AI from the FDA-approved label text and reviewed by our pharmacy team before publication. Sanofi Pasteur Inc. is the representative DailyMed label linked for verification and dates. This is general education, not medical advice: always talk to your doctor or pharmacist about your own medicines. How we build and review drug pages →